Blood circuit for a dialysis machine and corresponding dialysis machine

ABSTRACT

A blood circuit ( 1 ) for a dialysis machine is made form plastic material and is provided with a metallic plate ( 30 ), which is applied to an external face of the blood circuit ( 1 ) and is connectable to a voltage generator ( 34 ) in such a way as to form a capacitor, in which the plate ( 30 ) and the blood act as the capacitor plates and the plastic material acts as the dielectric.

DESCRIPTION

[0001] The present invention relates to a blood circuit for a dialysismachine.

[0002] As is known, blood consists of a liquid component, called theblood plasma, and a corpuscular component formed by the blood cells,including the red corpuscles among other types. In renal insufficiency,the blood contains, in addition to the aforesaid components, particlesof low molecular weight (referred to below as the solute), which have tobe eliminated by a dialysis treatment carried out by means of a dialysismachine.

[0003] A dialysis machine of a known type generally comprises a bloodcircuit, a dialysate circuit, and a filter which is connected to theaforesaid circuits and comprises a blood compartment and a dialysatecompartment, which are separated from each other by a semi-permeablemembrane, and through which pass, respectively, the blood to be treatedand the dialysate, generally flowing in counter-current mode, when themachine is in operation.

[0004] During the dialysis treatment, the unwanted particles containedin the blood migrate from the blood compartment to the dialysatecompartment both by diffusion and by convection, as a result of thepassage of some of the liquid contained in the blood towards thedialysate compartment. The patient will therefore have lost some weightby the end of the dialysis process.

[0005] The blood circuit is connected to the patient by means of anarterial needle and a venous needle, which are inserted into a fistulaformed in the patient's cardiovascular system, and are used,respectively, to collect the blood to be treated and to return thetreated blood to the patient's cardiovascular system. The blood circuitcomprises two expansion chambers (or droppers), one located in thearterial branch and one in the venous branch.

[0006] In a known method for detecting the detachment of the venousneedle from the patient and preventing blood loss due to the detachmentof the venous needle, an electric current is injected into the bloodcircuit in such a way that the detachment of the venous needle iscomparable to the opening of a circuit. Thus, by measuring the variationof electric current flowing in the blood circuit it is possible todetect the detachment of the venous needle.

[0007] For example, patent application WO 99/12588 describes a method inwhich the blood circuit is connected to an electrical circuit to injecta current into a closed circuit consisting of the blood circuit and thepatient's cardiovascular system, and to measure, by means of a measuringinstrument located in the aforesaid blood circuit, the variations ofcurrent caused by the detachment of one or both of the needles. In thismethod, the current injection and the measuring of the variation ofcurrent are carried out by means of inductive couplings located in theblood circuit, in other words by means of windings formed around theextracorporeal blood circuit at specified points of this circuit.

[0008] The placing of the windings around the blood circuit gives riseto problems of a practical nature, since the coupling between the bloodcircuit and the electrical circuit is laborious to set up and requires acertain amount of the operator's time.

[0009] The object of the present invention is to provide a blood circuitwhich can be coupled in a simple and practical way to an electricalcircuit.

[0010] According to the present invention, a blood circuit is providedfor a dialysis machine, the blood circuit being made from plasticmaterial and being characterized in that it comprises a metallic plateapplied to an external face of the said blood circuit, the said platebeing connectable to a voltage generator in such a way as to form acapacitor, in which the said plate and the blood act as the capacitorplates and the plastic material acts as the dielectric.

[0011] The advantages of the present invention are due to thereplacement of the inductive coupling by a capacitive coupling, whichcan be formed simply by applying a metallic plate to the blood circuitat the point of the blood circuit where the electrical connection is tobe made.

[0012] The present invention also relates to a dialysis machine forproviding dialysis treatment to patients.

[0013] According to the present invention, a dialysis machine is madefor carrying out dialysis treatments on patients, the machine comprisinga blood circuit according to any one of the preceding claims, anelectrical cable and the said voltage generator for supplying, when inuse, an electric current through a preferential current-carrying circuitcomprising the blood circuit, the electrical cable and a patientconnected to the said blood circuit.

[0014] The present invention will now be described with reference to theattached drawings, which show a non-restrictive example of itsembodiment, in which,

[0015]FIG. 1 is a schematic view, with parts removed for clarity, of ablood circuit associated with a dialysis machine; and

[0016]FIG. 2 is a view, on an enlarged scale, of a detail of the circuitof FIG. 1.

[0017] In FIG. 1, the number 1 indicates the whole of a blood circuitfor a dialysis machine 2.

[0018] The machine 2 is provided with a machine casing 3, which supportsa rotor 4 which, in conjunction with a circuit 1, forms a peristalticpump 5; a filter 6, which is shown in broken lines and comprises asemi-permeable membrane 7 which separates a blood compartment 8 from adialysate compartment 9; and a dialysate circuit 10, which is shown inbroken lines and is connected to the dialysate compartment 9 of thefilter 6.

[0019] The circuit 1 has an arterial branch 11, a venous branch 12 and abox 13, which comprises an expansion chamber 14 in the arterial branch11, an expansion chamber 15 in the venous branch 12, and a channel 16located above the expansion chambers 14 and 15. The arterial branch 11comprises a portion 17, which extends between the expansion chamber 14and a connector 18 for connecting the arterial branch 11 to an arterialneedle AN, a portion 19, which is bent into a U-shape around the rotor 4to form the peristaltic pump 5, and whose ends are connected to theexpansion chamber 14 and to the channel 16, and a portion 20 whichconnects the channel 17 to the blood compartment 8 of the filter 6. Thevenous branch 12 has a portion 21, which extends between the expansion15 and a connector 22 for connecting the venous branch 12 to a venousneedle VN, and a portion 23, which extends between the expansion chamber15 and the blood compartment 8 of the filter 6.

[0020] In operation, the arterial needle AN and the venous needle VN areconnected to a fistula of a patient P, in order, respectively, tocollect the blood from the patient P and return it to him.

[0021] The box 13 is made from rigid transparent material, while thearterial branch 11 and the venous branch 12 are made from transparentflexible plastic material.

[0022] With reference to FIG. 2, the box 13 comprises two principalopposed walls 24 (only one of which is shown in the attached figures), aperimetric wall 25 located between the principal walls 24, a partition26 for separating the channel 16 from the expansion chambers 14 and 15,and a partition 27 for separating the expansion chambers 14 and 15 fromeach other.

[0023] During dialysis treatment, the blood occupies lower portions 28of the corresponding expansion chambers 14 and 15, while the upperportions 29 are occupied by air. In practice, the division of each ofthe chambers 14 and 15 into a lower portion 28 and an upper portion 29is marked by the level L of the blood in each of the expansion chambers14 and 15. During the dialysis treatment, the level L is keptessentially constant by means of known control devices which areassociated with the dialysis machine 2 and are not illustrated.

[0024] Each chamber 14 and 15 has a corresponding pressure sensor PSlocated in the upper portion 29, while the expansion chamber 15 has aconductive element in the form of at least a metallic plate 30, which isfixed to the lower portion 28 of the box 13.

[0025] Note that the conductive element may alternatively be a plasticelement having conductive properties, such as a plastic elementembedding conductive particles and/or conductive fibres and/orconductive filaments. Suitable materials for the particles, fibres,filaments can be Alluminium or Carbon.

[0026] The plate 30 is a strip of metallic material, and has a face indirect contact with the external face of the wall 24 and a face which isopposite the preceding one and supports an electrical connector 31. Thenumber 32 indicates an electrical cable provided with an electricalconnector 33 which can be joined to the connector 31 to connect theplate 30 to a voltage generator 34. With reference to FIG. 1, theelectrical cable 32 also connects the voltage generator 34 to thepatient P.

[0027] During the dialysis treatment, the blood is directed along thearterial branch 11 and the venous branch 12 in the direction shown bythe arrows in FIG. 1, and passes through the blood compartment 8 of thefilter 6 and the expansion chambers 14 and 15 of the box 13. The bloodaccumulates in the lower portions 28 of the expansion chambers 14 and15.

[0028] In order to detect the detachment of the venous needle VN, thecable 32 is connected to the plate 30 through the connectors 31 and 33,and is connected to the patient P and is supplied by the generator 34.

[0029] Since blood and the plate 30 are conductors of electric current,and the plastic material from which the box 13 is made is an insulatingmaterial, the presence of the plate 30 on the portion 28 of theexpansion chamber 15 effectively forms a capacitor, in which the plate30 and the blood are the opposing plates and the wall 24 is thedielectric.

[0030] The applicant has found that the connections shown in FIG. 1between the cable 32, the patient P and the blood circuit 1 provide apreferential circuit for the flow of the electric current, comprisingthe cable 32, the patient P, the portion 21 of the venous branch 12 andthe lower portion 28 of the expansion chamber 15.

[0031] Consequently, any discontinuity between the venous branch 12 andthe patient P causes a significant variation of the current in theaforesaid preferential electrical circuit. This variation can bemeasured, for example, by measuring the variation of voltage across theterminals of an impedance located in the branch 32.

[0032] The detachment of the venous needle VN is therefore comparable tothe opening of the aforesaid preferential electrical circuit, and iseasily detectable by measuring the voltage.

[0033] The applicant has also found that the preferential electricalcircuit does not differ from that described above when the end of thecable 32 connected to the patient P is connected to earth and thecurrent flowing in the preferential circuit exceeds 10 kHz. In thiscase, the preferential electrical circuit is completed via the earth,regardless of whether the patient P is connected directly to earth or isnot connected directly to earth. In the second case, the patient P inconjunction with the earth forms a capacitor, and, in electric terms,behaves in an essentially equivalent way to a patient P directlyconnected to earth when the frequency of the current flowing in thepreferential circuit exceeds 10 kHz.

[0034] In a variant which is not shown, both of the expansion chambers14 and 15 are provided with corresponding plates 30 for coupling boththe arterial branch 11 and the venous branch 12 to the cable 32 by meansof corresponding electrical connectors 33.

[0035] In a further variant which is not shown, the plate 30 can belocated in any one of the portions of the venous branch 12 and thearterial branch 12, and can have an annular shape.

[0036] The present description implies that one or more plates 30 can belocated at any point of the blood circuit 1 to electrically connect anelectrical cable to the blood circuit 1 by means of a capacitivecoupling.

[0037] The example which is described and illustrated is particularlyadvantageous, since it simplifies the electrical coupling between theelectrical circuit and the blood circuit, while requiring only a singleelectrical connection.

1. Blood circuit for a dialysis machine, the blood circuit (1) beingmade from plastic material and being characterized in that it comprisesan electrically conductive element (30) applied to an external face ofthe said blood circuit (1), the said conductive element (30) beingconnectable to a voltage generator (34) in such a way as to form acapacitor, in which the said conductive element (30) and the blood actas the capacitor plates and the plastic material acts as the dielectric.2. Circuit according to claim 1, characterized in that the saidconductive element is a metallic plate (30) and has one face placed incontact with the said blood circuit (1).
 3. Circuit according to claims1 or 2, characterized in that the said conductive element comprises afirst electrical connector (31), the generator (34) having an electricalcable (32) provided with a second electrical connector (33) which can becoupled to the said first electrical connector (31).
 4. Circuitaccording to any one of claims 1 to 3, characterized in that itcomprises an arterial branch (11) and a venous branch (12) made fromflexible plastic material and a box (13) made from transparent plasticmaterial.
 5. Circuit according to claim 4, characterized in that thesaid conductive element (30) is placed in contact with an external faceof the said venous branch (11).
 6. Circuit according to claim 4,characterized in that the said conductive element (30) is placed on anexternal face of the said box (13).
 7. Circuit according to claim 6,characterized in that the said box (13) comprises two principal walls(24) and a perimetric wall (25); the said wall (30) being located alongan external face of one of the said principal walls (24).
 8. Circuitaccording to claim 6 or 7, characterized in that the said box (13)comprises an arterial expansion chamber (14) connected to the arterialbranch (11) and a venous expansion chamber (15) connected to the venousbranch (11); the arterial expansion chamber (14) and venous expansionchamber (15) being provided with corresponding portions (28) which areoccupied by blood when in use, the conductive element (30) being appliedto an external face of the said venous chamber (15) in the area of thesaid portion (28).
 9. Circuit according to claim 8, characterized inthat it comprises a further electrically conductive element (30), thesaid further electrically conductive element (30) being applied to anexternal face of the said arterial expansion chamber (14) in the area ofthe said portion (28).
 10. Circuit according to claim 9, characterizedin that said further electrically conductive element is a metallicplate.
 11. Circuit according to claim 1 or to claim 9, characterized inthat said electrically conductive element and/or said furtherelectrically conductive elements are made of plastics embeddingelectrically conductives bodies.
 12. Circuit according to claim 11,characterized in that said electrically conductive bodies compriseelectrically conductive fibers.
 13. Circuit according to claim 11,characterized in that said electrically conductive bodies compriseelectrically conductive particles.
 14. Circuit according to claim 11,characterized in that said electrically conductive bodies compriseelectrically conductive filaments.
 15. Dialysis machine for carrying outdialysis treatments on patients (P), the machine comprising a bloodcircuit (1) according to any one of the preceding claims, an electricalcable (32) and the said voltage generator (34) for supplying, when themachine is in use, an electrical current through a preferentialelectrical circuit comprising the blood circuit (1), the electricalcable (32) and a patient (P) connected to the said blood circuit (1).